1. Field of the Invention
The present invention relates to a method for transmitting scheduling information, and more particularly, to a method for transmitting scheduling information in a hierarchical cell structure.
2. Discussion of the Related Art
A femtocell base station, which is a small-size version of a macrocell base station, performs most functions of the macrocell base station. The femtocell base station may be installed in an area covered by the macrocell base station or may be installed in a shadow area that is not covered by the macrocell base station. The femtocell base station has a network structure that operates independently. A far greater number of femtocell base stations than relay base stations are installed indoors or outdoors. A list of neighboring base stations that a base station transmits to a mobile station does not include a list of femtocell base stations since the amount of information of the femtocell base stations is too great.
FIG. 1 illustrates a configuration of a wireless communication system including femtocell base stations.
As shown in FIG. 1, the wireless communication system includes femtocell base stations 110, a macrocell base station 120, a femto network gateway (FNG) 130, an access service network (ASN) 140, and a connectivity service network (CSN) 150. The macrocell base station 120 is a general base station of the conventional wireless communication system.
Each femtocell base station 110 is a small-size version of the macrocell base station 120 and performs most functions of the macrocell base station 120. The femtocell base station 110 directly connects to a transmission control protocol/Internet protocol (TCP/IP) network and operates independently as the macrocell base station 120 does. The coverage of the femtocell base station 110 is about 0.1 to 30 m and each femtocell base station 110 can accommodate about 10 to 20 mobile stations. The femtocell base station 110 may also use the same frequencies as the macrocell base station 120 or may use different frequencies from the macrocell base station 120.
The femtocell base station 110 may be connected to the macrocell base station 120 through an R1 interface and can receive a downlink channel from the macrocell base station 120 and can transmit a control signal to the macrocell base station 120.
The macrocell base station 120 can cover an indoor or shadow area that is not covered by the macrocell base station 120 and can support high data rates. The femtocell base station 110 may be installed in an overlay fashion in a macrocell and may also be installed in a non-overlay fashion in an area that is not covered by the macrocell base station 120.
The femtocell base station 110 is classified into two types. The first type is a closed subscriber group (CSG) femtocell base station and the second type is an open subscriber group (OSG) femtocell base station. The CSG femtocell base station groups mobile stations capable of accessing it and assigns a CSG identification (ID) to the group of mobile stations and allows only mobile stations assigned the CSG ID to access the CSG femtocell base station. The OSG femtocell base station is a base station which can be accessed by every mobile station.
As a gateway that controls the femtocell base station 110, the FNG 130 is connected to the ASN 140 and the CSN 150 through an Rx interface and an Ry interface. The femtocell base station 110 can receive a service from the CSN 150 through the FNG 130 and a mobile station connected to the femtocell base station 110 can receive services of functions such as authentication and IMS from the FNG 130 or the CSN 150.
The CSN 150 provides the mobile station with connection to an application service such as the Internet or VoIP service. The ASN 140 controls the macrocell base station 120 and manages connection between the macrocell base station 120 and the CSN 150.
FIG. 2 illustrates an example of a conventional method for perform scheduling at a macrocell base station.
The scheduling method shown in FIG. 2 can be considered an extension of the conventional macro-based scheduling method to a hierarchical cell structure. In the conventional method, a macrocell base station receives feedback information (for example, channel information and traffic information) from macro users and allows the users to perform communication using a specific frequency at a specific timing. When this method is extended and applied to the hierarchical cell structure, the macrocell base station can receive all necessary information from femto user and macro user. Here, the femto user can transmit feedback information including a parameter associated with a relation with the femtocell base station rather than a relation with the macrocell base station. Upon receiving the feedback information from the femto user and macro user, the macrocell base station can allocate resources to each user. The macrocell base station can operate while discriminating between the macro user and femto user.
Here, the macro user may feed the necessary information back to the macrocell base station according to the conventional method. The femto user may also feedback the necessary information to the macrocell base station according to the conventional method. Alternatively, the femtocell base station may collect and feedback necessary information of the femto user to the macrocell base station. The fact that the macrocell base station has allocated resources to the femto user indicates that the macrocell base station allows the femto user to communicate with the femtocell base station using the resources.
FIG. 3 illustrates a conventional frame structure for transmitting scheduling information at a macrocell base station.
The macrocell base station can transmit scheduling information to macro user and femto user on a subframe by subframe basis using a macro PDCCH. This conventional scheduling method has problems in that the femtocell base station passively operates to perform functions similar to those of a relay station and cannot perform free scheduling. The conventional scheduling method also has problems in that the scheduling overhead of the macrocell base station is very high and mobile stations with low sensitivity of reception from the macrocell base station cannot receive scheduling information from the macrocell base station.